This invention relates to a dielectric thin film of silicon and titanium oxide used as an insulating layer for a capacitor in a semiconductor DRAM. A method of manufacturing such a dielectric thin film is also disclosed.
In the past, as the insulating layer of a DRAM capacitor, a film of either SiO.sub.2 or Si.sub.3 N.sub.4 has been used. These films have small leakage current, high breakdown voltage, and high reliability. However, with a dielectric constant of only 5, these films do not obtain enough capacitance for DRAMs of more than 64M bit having a small area for the capacitor. Thus, instead of using SiO.sub.2 and Si.sub.3 N.sub.4 as the material for the insulating layer of the capacitor, Ta.sub.2 O.sub.5, with a dielectric constant 5 to 6 times larger than that of SiO.sub.2, has been noted, and its application has been investigated. However, Ta.sub.2 O.sub.5 thin film has the disadvantage that its leakage current is large compared with an SiO.sub.2 layer. Ta.sub.2 O.sub.5 thin film also has the disadvantage of the dielectric constant sharply decreasing in the vicinity of 100 .ANG. thickness, which is typical as the insulating layer in the actual DRAM. The dielectric constant of TiO.sub.2 goes down as a TiO.sub.2 thin film becomes thinner. However, this does not matter, due to the high dielectric constant of TiO.sub.2 (being about 100) in the bulk state. Thus, the film can be used as an insulating layer of the capacitor. Nevertheless, TiO.sub.2 film has the disadvantage of a large leakage current. Thus, in the application of a DRAM of more than 64M bits, the SiO.sub.2 layer or Si.sub.3 N.sub.4 layer does not have enough capacitance due to the small dielectric constant, despite the small leakage current and high reliability. Also, the TiO.sub.2 film has a large dielectric constant and can obtain sufficient capacitance, but, still, is of low reliability on account of its large leakage current. Accordingly, the films comprised of SiO.sub.2, Si.sub.3 N.sub.4 and TiO.sub.2 are not practical for the insulation layer of the capacitor of the high-density DRAM.